The program assumes that all frequencies are in radians/sec, unless a HRTZ data record has been used to change this to Hertz (cycles/sec).
2 5 7 11 21 31 41 51 61
- --- -- ---- ---------- -------- -------- -------- -------- --------
|X| | |JONS|XXXXXXXXXX| | | | | |
- --- -- ---- ---------- -------- -------- -------- -------- --------
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| | | | | | | |
| | | | | | | (5)Peak Frequency
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| | | | | | |_(4)Alpha(F10.0)
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| | | | | |_(3)Gamma(F10.0)
| | | | |
| | | | |_(2)Finish Frequency(F10.0)
| | | |
| | | |_(1)Start Frequency(F10.0)
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| | |_Compulsory Data Record Keyword(A4)
| |
| |_Optional User Identifier(A2)
|
|_Compulsory END on last data record in data category(A3)
(1)-(2) Start/Finish Frequency - The lowest/highest frequency at which the spectrum is defined.
If these fields are left blank, defaults will be assumed as follows:
Start frequency = Peak frequency * (0.58+(γ-1.0)*0.05/19.0)
Finish frequency is evaluated numerically so that approximately 99% of the spectral energy is included.
(3)-(5) Gamma, Alpha and Peak Frequency. Note that even if Hz is used to define the frequencies, Alpha has units of rad^4.
The JONSWAP wave spectrum can be used to describe a wave system where there is an imbalance of energy flow (i.e. sea not fully developed). This is nearly always the case when there is a high wind speed.
It may be considered as having a higher peak spectral value than the Pierson-Moskowitz spectrum (The PSMZ Data Record - Pierson-Moskowitz Spectrum) but is narrower away from the peak in order to maintain the energy balance.
Parameterization of the classic form of the JONSWAP spectrum (with parameters of fetch and wind speed) was undertaken by Houmb and Overvik (BOSS Trondheim 1976,Vol 1). These parameters are used by Aqwa. These empirical parameters are termed gamma (3), alpha (4) and peak frequency (5) (the frequency at which the spectral energy is a maximum).